This invention relates to handling of materials on pallets. It relates to palletizing materials and subsequently depalletizing those materials, all with a minimum amount of manual lifting on the part of attending labor or machine operators. The invention relates specifically to methods for palletizing and depalletizing thin-section materials, and especially loose stacks of printed materials such as newspapers, signatures, sheets of paper, magazines and the like; including stacks of in-process material. Individual elements of the material may be as thin as a single sheet of paper or as thick as a magazine or a book. Particularly with reference to newspapers and signatures, the loose stacks are typically compressible and of uneven height.
Apparatus for palletizing bundles of newspaper is known in the art. A conventional palletizer for boxes or cartons may use a horizontally, reciprocally movable stripper plate for carrying boxes to a position above a pallet onto which the boxes are to be loaded. The stripper plate is then withdrawn from beneath the boxes, thereby depositing them onto the pallet. Retaining means are used for preventing the boxes from moving with the stripper plate as it is withdrawn. Such retaining means commonly include a bar which abuts the side of the boxes facing the direction of stripper plate withdrawal. Structures of this general nature are disclosed in, for example, U.S. Pat. Nos. 3,149,732 Gagnon et al and 3,833,132 Alduk.
In co-pending application Ser. No. 770,268, filed Aug. 28, 1985, now U.S. Pat. No. 4,704,060, and herein incorporated by reference, there is disclosed palletizing apparatus for palletizing stacks of loose materials such as newspapers, signatures, sheets of paper, and the like. In that application, there is disclosed a plate and plate movement means, for depositing material onto a pallet or onto a partial load of material on a pallet. In that teaching, any underlying compressible materials may be compressed by the plate during the process of depositing the material. Both the material being deposited and the underlying material may be prevented from moving with the plate, by first and second projection means projecting into recessed portions of the top and bottom surfaces of the plate. The pallet load which results from loading a pallet as disclosed therein consists of a plurality of stacks extending from the underlying pallet, or a slip sheet thereon, to the upper extremity of the stack, typically the top of the pallet load. Within that environment of continuous stacks, unloading the material from the pallet is typically done by manual labor. In that process, the material is removed in a series of steps limited by the amount of material a person can manually lift at one time.
Alternatively, unloading might be done by a depalletizer wherein essentially an entire layer of the material is pushed, or swept, off the pallet at one time. The latter case of using a depalletizer is preferred in that it reduces the chance of back injury caused by excessive manual labor at the point of depalletizing, along with the associated savings in labor costs.
However, conventional palletizers do not have the capability to stack loose materials such as newspaper and the like, except as dislosed in above-mentioned application Ser. No. 770,268, now U.S. Pat. No. 4,704,060. And to the extent newspapers are stacked on a pallet as in application Ser. No. 770,268, now U.S. Pat. No. 4,704,060, there is not any conventionally known means for removing all of the load with known pallet unloading apparatus unless the load is quite small.
One problem with handling loose materials with a pallet unloading apparatus is that each unit of the load of material on the pallet must be acted upon in some way, by the apparatus, to affect the desired movement.
A load unit is herein defined as any article, or group of articles, of the load, requiring a separate external force to cause it to move. Thus a single loose sheet of paper is a unit as is a bound bundle of papers. For assembled documents, such as newspaper, each document is generally a unit of the load.
With sheets of paper, each sheet can be a unit of the load. With the small thickness of, for example, paper, it is easy for sheets, near the bottom of a stack, to be missed by that material handling apparatus which functions by action on a side of the stack, at the edges of the sheets. Yet, efficient material handling of thin sheets typically is done through interactions at the sheet edges.
Another problem with handling stacks of loose sheet materials with a pallet unloading apparatus is that only a limited stack height can be moved by pushing on a side of the stack without undue risk of toppling the stack. So some means should be provided to limit the height of an individual stack in the pallet load without the height of the individual stack determining the maximum overall amount of material which may be placed on a pallet to make up the pallet load.
It is an object of this invention to provide a method of handling material on a pallet which enables the stacking by a palletizer on a pallet, of thin and, optionally compressible, materials such as loose papers, magazines or the like, optionally in discrete layers; such that they can subsequently be removed from the pallet, in the same discrete layers, by an appropriately configured depalletizer.
As previously mentioned, palletizing apparatus useful for placing stacks of loose sheets on a pallet is disclosed in pending application Ser. No. 770,268, now U.S. Pat. No. 4,704,060, filed Aug. 28, 1985. Depalletizing apparatus and methods, and a special spacing sheet, useful with stacks of loose sheets, are disclosed in pending application Ser. No. 888,511, filed Jul. 23, 1986, now abandoned and refiled as Ser. No. 07/102,386. Palletizing apparatus is also disclosed in the following United States patents, previously cited in application Ser. No. 770,268.
______________________________________ Locke et al. 2,875,907 Woodcock 2,875,908 Keyes 2,878,948 Gagnon et al. 3,149,732 Jeremiah 3,166,203 Kampert 3,257,006 Grasvoll 3,594,977 Larson 3,606,310 Brockmuller et al. 3,637,093 Grasvoll 3,648,857 Carlson 3,669,282 Alduk 3,833,132 Golantsev 3,837,140 Kelley 4,030,618 Schmitt 4,162,016 Schmitt 4,195,959 Pantin et al. 4,205,934 Faltin 4,230,311 Donnelly 4,234,280 Meratti et al. 4,255,074 Cox et al. 4,342,531 Sylvander 4,383,788 Werkheiser 4,422,549 Werkheiser 4,439,084 Wise 4,477.067 ______________________________________